Is there any way to clean up my overflowing email account?

My school email account is filled up well above %100 becuase we only get like 20MB of space. BUT I cannot delete any of the messages because they have to be moved to the trash first and it wont let me overflow my Inbox. Is there any way I can override this or check my email through another service that will let me clear my Inbox?

Is there any way to clean up my overflowing email account?
Call the school tech support.
Reply:Does your school email service have a forwarding service? You can try using the forwarding so that your emails will get sent to another email like your Yahoo account! Try this ok?